It slowly makes the ground softer making it easier for it to dissolve
This is true.
The definition of megalopolis is that it is a large urban area, huge and densely populated. St. Petersburg is definitely one, however, Miami is relatively small compared to other megalopolises so it might not fall within that category.
A bay is a water-body bounded by land on all three sides, and a peninsula is a piece of land sticking off a bigger piece of land and surrounded by water on all three sides.
